Low noise is the first priority, section balance is also impt. I found real sonic improvements with NOS versions of all the preamp tubes, though certain of the 6SN7s impact that more than others. Tube dampers also work well in this application - I use Herbies. There are 8 12AT7s in the MP-1 with phono - consider yourself lucky :-).
Ralph may tell you there are no more quiet NOS 12AT7s, but I have real good results with these:
* Siemens Halske 3 Mica E81CC (Tubemonger.com) - very clear w/ nicely extended top end and transient definition
* Sylvania 6201 (Upscale Audio)- excellent all around
* Mullard CV4024 (Jim McShane)- rich instrumental and vocal timbre
Tim
Ralph may tell you there are no more quiet NOS 12AT7s, but I have real good results with these:
* Siemens Halske 3 Mica E81CC (Tubemonger.com) - very clear w/ nicely extended top end and transient definition
* Sylvania 6201 (Upscale Audio)- excellent all around
* Mullard CV4024 (Jim McShane)- rich instrumental and vocal timbre
Tim